PM8621 datasheet(160/184 Pages) PMC

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NSE-8G™ Standard Product Data Sheet

Preliminary

Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use

159

Document ID: PMC-2010850, Issue 1

Consider a request to route an octet from ingress port i to egress port j, where i and j range from

0 to 3, over four ports corresponding to the four SBS devices. To make this connection, we must

find a timeslot in the NSE-8G which can accept an octet from the ingress SBS and send an octet

to the egress SBS. If the NSE-8G has these two slots free in the same timeslot, then the SBSs

must also have the corresponding slot free. The actual routing of the sample is accomplished in

several steps. The octet is:

1. mapped to the free timeslot by the ingress SBS port,

2. picked up by the NSE-8G in that timeslot on the port from the ingress SBS and mapped to the

port which leads to the egress SBS,

3. picked up by the egress SBS in the expected timeslot.

It may not be possible to find a free time which connects the ingress SBS to the egress SBS, even

though both SBS devices have unused capacity into the NSE-8G core (the ingress SBS may have

a free timeslot at time i and the egress SBS may have a free timeslot at time j, but i ~= j). Such

cases require a more complex algorithm which is capable of disconnecting and reconnecting other

connections to make space for the new i to j connection. (Disconnection and reconnection of

other connections is done hitlessly by NSE/SBS fabrics.) This more sophisticated algorithm is

described in the remainder of this section.

12.13.3 Bi-partite graphs

A general solution to the connection problem is a schedule where each connection is assigned to

one of the 9720 timeslots in each time stage such that no two connections conflict. This solution

then maps to physical switch settings for the SBS and NSE-8G devices. The following definitions

allow us to represent the problem as an abstract graph problem:

1. Draw a graph where each input and output port is represented as a node.

2. Partition the graph so that all of the input ports are in one partition and all the output ports

are in the other.

3. Draw an edge from an input node to an output node if there is a connection from the

corresponding input port to the corresponding output port.

This results in a bipartite graph where each node has a maximum degree of 9720 (the total

number of possible connections from/to a port). A subset of this problem (6 nodes, 2 timeslots) is

illustrated in Figure 29. We want to assign the edges (connections) to timeslots such that no

coincident edges are assigned to the same timeslot. Notice that a solution to the problem consists

of a permutation (or partial permutation) mapping of input nodes onto output nodes for each of

the timeslots. These permutation mappings correspond to one set of switch settings for the NSE-

8G devices.

PM8621 Datasheet(PDF) 160 Page - PMC-Sierra, Inc